Chiral preferences exist in proline-substituted serine octamers. For ions of [L-Ser6 + Pro2]H(+), the stability preference is [L-Ser6 + L-Pro2]H(+) > [L-Ser6 + D-Pro2]H(+) > [L-Ser6 + L-Pro1 + D-Pro1]H(+). Infrared photodissociation (IRPD) experiments were performed for the observed proline-substituted octamer ions in the range from 2700 to 3750 cm(-1). Chiral differentiation was achieved using the IRPD method, and the progressive changes in IRPD spectra due to the substitution were also reflected.